Utilisation of Coir Geotextiles for Unpaved Roads and Embankments

The increasing tempo of construction activity the world over creates heavy pressure
on existing land space. The quest for new and competent site often points to the needs
for improving existing sites, which are otherwise deemed unsuitable for adopting
conventional foundations. This is accomplished by ground improvement methods,
which are employed to improve the quality of soil incompetent in their natural state.
Among the construction activities, a well-connected road network is one of the basic
infrastructure requirements, which play a vital role for the fast and comfortable
movement of inter- regional traffic in countries like India.One of the innovative ground improvement techniques practised all over the world is
the use of geosynthetics, which include geotextiles, geomembranes, geogrids, etc .
They offer the advantages such as space saving, enviromnental sensitivity, material
availability, technical superiority, higher cost savings, less construction time, etc .
Because of its fundamental properties, such as tensile strength, filtering and water
permeability, a geotextile inserted between the base material and sub grade can
function as reinforcement, a filter medium, a separation layer and as a drainage
medium. Though polymeric geotextiles are used in abundant quantities, the use of
natural geotextiles (like coir, jute, etc.) has yet to get momentum. This is primarily
due to the lack of research work on natural geotextilcs for ground improvement,
particularly in the areas of un paved roads. Coir geotextiles are best suited for low cost
applications because of its availability at low prices compared to its synthetic
counterparts. The proper utilisation of coir geotextilcs in various applications demands large quantities of the product, which in turn can create a boom in the coir
industry. The present study aims at exploring the possibilities of utilising coir
geotextiles for unpaved roads and embankments.The properties of coir geotextiles used have been evaluated. The properties studied
include mass per unit area, puncture resistance, tensile strength, secant modulus, etc .
The interfacial friction between soils and three types of coir geotextiles used was also
evaluated. It was found that though the parameters evaluated for coir geotextiles have
low values compared to polymeric geotextiles, the former are sufficient for use in
unpaved roads and embankments. The frictional characteristics of coir geotextile - soil
interfaces are extremely good and satisfy the condition set by the International
Geosynthetic Society for varied applications.The performance of coir geotextiles reinforced subgrade was studied by conducting
California Bearing Ratio (CBR) tests. Studies were made with coir geotextiles placed
at different levels and also in multiple layers. The results have shown that the coir
geotextile enhances the subgrade strength. A regression analysis was perfonned and a
mathematical model was developed to predict the CBR of the coir geotextile
reinforced subgrade soil as a function of the soil properties, coir geotextile properties,
and placement depth of reinforcement.The effects of coir geotextiles on bearing capacity were studied by perfonning plate
load tests in a test tan1e This helped to understand the functioning of geotextile as
reinforcement in unpaved roads and embankments. The perfonnance of different
types of coir geotextiles with respect to the placement depth in dry and saturated
conditions was studied. The results revealed that the bearing capacity of coir-reinforced soil is increasing irrespective of the type of coir geotextiles and saturation
condition.The rut behaviour of unreinforced and coir reinforced unpaved road sections were
compared by conducting model static load tests in a test tank and also under repetitive
loads in a wheel track test facility. The results showed that coir geotextiles could
fulfill the functions as reinforcement and as a separator, both under static and
repetitive loads. The rut depth was very much reduced whik placing coir geotextiles
in between sub grade and sub base.In order to study the use of Coir geotextiles in improving the settlement
characteristics, two types of prefabricated COlf geotextile vertical drains were
developed and their time - settlement behaviour were studied. Three different
dispositions were tried. It was found that the coir geotextile drains were very effective
in reducing consolidation time due to radial drainage. The circular drains in triangular
disposition gave maximum beneficial effect.In long run, the degradation of coir geotextile is expected, which results in a soil -
fibre matrix. Hence, studies pertaining to strength and compressibility characteristics
of soil - coir fibre composites were conducted. Experiments were done using coir
fibres having different aspect ratios and in different proportions. The results revealed
that the strength of the soil was increased by 150% to 200% when mixed with 2% of
fibre having approximately 12mm length, at all compaction conditions. Also, the
coefficient of consolidation increased and compression index decreased with the
addition of coir fibre.Typical design charts were prepared for the design of coir geotextile reinforced
unpaved roads. Some illustrative examples are also given. The results demonstrated that a considerable saving in subase / base thickness can he achieved with the use of
eoir geotextiles, which in turn, would save large quantities of natural aggregates.

Description:

Division of Civil Engineering,
Cochin University of Science and Technology